A Study On The Modification Of Spinel Lithium Manganese By Ion Doping

This dissertation is intending to investigate the modification of spinel lithiummanganese cathode material for lithium-ion batteries by ion doping, so as to improve itselectrochemical performance. Efforts were made to optimize the preparation techniques ofspinel LiMn2O4 with solid-state method. Mono-cation doping, binary-cation doping andmulti-cation doping methods were adopted to modify the spinel LiMn2O4 cathode. Theireffects on the crystal structure and electrochemical properties of the result spinel lithiummanganese were studied respectively. The action mechanism of ion doping was alsoprobed. The optimization of spinel LiMn2O4 preparation techniques was studied by means ofTG-DTA, XRD, SEM, particle size distribution, specific surface area analysis andelectrochemical charge-discharge tests. Nano-EMD and spinel Mn3O4 were used as theMn sources for the first time to synthesize spinel LiMn2O4 and the produced LiMn2O4were compared with the product from EMD and MnCO3. The optimal Li/Mn proportionswere inspected with EMD and Mn3O4 as the Mn sources respectively. Mn3O4 weredecided to be the optimum Mn source simultaneously. The effects of doping concentration on the physicochemical structure andelectrochemical performance of produced cathode were systematically investigated withseveral kinds of cations mono-doped separately. Attempts were made for the first time tobreak the traditional concepts in choosing the doping ions for the spinel lithiummanganese modification. The lanthanide ion La3+, which has the much larger ionic radiusthan Mn3+ while has much stronger Mn-O bond energy and higher octahedral sitepreference, was introduced to modify spinel lithium manganese. It was proved that theLa3+ doping is propitious to the produced spinel cathode. The spinel lithium manganesewere compared with different cations used as doping ions at a same doping concentration.The binary-cation doping and multi-cation doping have much better effects on improvingthe electrochemical performance especially high-temperature(55℃) performance ofproduced spinel cathode. The crystal structure characteristics and electrochemicalproperties of spinel lithium manganese cathode with F- and Cl- anion doped were lookedinto respectively. The performances of above two series of anions doped spinel cathodewere also probed when the charge-discharge rate is 0.5C. The modified spinel cathodewith some cations and anions multiplex doped were synthesized for the first time. Bychoosing the doping ions combination scheme and controlling the doping quantum,perfect spinel lithium manganese cathode were produced which have high initial capacityas well as good cycle performances at both room temperature and high temperature. The causes for the capacity fading of spinel lithium manganese were discussed. Theaction mechanism of ion doping was analyzed in terms of the crystal structure andelectrochemical properties. The differential curves dE/dQ ~ Q were made for the first timeto analyze the change in potential flat after ion-doping modification. The thermodynamicand kinetic equations were derived for the first time, which described the electrochemicalreaction of Li+ insetting into the spinel cathode.